1. Field of the Invention
The present invention relates to a reference electrode having an internal electrode in an internal filling solution, and more particularly to improvements that avoid blocking of a liquid junction.
2. Description of Related Art
When a reference electrode such as a silver/silver chloride is in operation, soluble silver ions (Ag+) can leach from the silver/silver chloride electrode, and dissolved chloro complex ions (such as AgCl2−) can be formed by the following reactions:AgCl+Cl−⇄AgCl2−  (1)AgC2−+Cl−⇄AgC32−  (2)
If such chloro complex ions meet a low chloride ion water at the liquid junction, a reaction can proceed in the direction from right to left according to each formula above and consequently AgCl (silver chloride) can precipitate at the junction.
Particularly, in any continuous operation at a high temperature of 60° C. or above, the silver ions (Ag+) and the dissolved chloro complex ions (such as AgCl2−) may increase in concentration, and at a lowered temperature, they can form silver chloride, with which the liquid junction can be blocked. Specifically, in continuous operation at 100° C., the liquid junction can be blocked with silver chloride within several days. Interfering substances such as proteins, silver, mercury, and H2S contained in liquid analytes can also come through the liquid junction into the internal filling solution. In such a case, they can also cause a displacement of the internal electrode potential or react with the silver ions to form less soluble precipitates with which the liquid junction can be blocked.
Therefore, conventional techniques include periodically replacing the internal filling solution to prevent an increase in the content of the silver or chloro complex ions, and/or forcing the internal filling solution to leak so that intake of the liquid analyte can be prevented under pressure changes caused by thermal cycles.
However, the former conventional technique does not drastically eliminate the silver ion, a liquid junction-blocking factor, and the maintenance thereof is not so easy. The later conventional technique needs a complicated structure of the reference electrode that will cause an increase in cost, and is less effective in continuous operation.
The present invention has been made in light of the above-mentioned problems.